The production of refinery products such as the various oil fractions, fuels and solvents involve the preheating of crude oils to from 150.degree. C. to 350.degree. C. prior to distillation into various fractions followed by subsequent exposure of said fractions to higher temperatures of 350.degree. C. to 700.degree. C. As an illustration, most of the gasoline produced today is obtained by the thermal or catalytic cracking of heavier petroleum hydrocarbon feed stocks such as light or heavy gas oils, cycle stocks, virgin or topped crude oils, lub stocks, kerosene, and kerosene-gas oil mixtures. A number of different thermal and/or catalytic cracking processes are industrially used for this purpose. Although these various processes differ considerably as to the precise manner in which the heavier hydrocarbon molecules are cracked to yield gasoline, they all involve the heating of the hydrocarbon feed stock to a high temperature (150.degree.-370.degree. C.) and the passage of such heated stock, optionally mixed with a cracking catalyst, through heated tubes, reactors, convertors, and tower stills.
Regardless of the refinery process used, the distillation and/or cracking operation (particularly the former) always results in the formation of undesirable carbonaceous material which accumulates on the inner surfaces of the process equipment, e.g., preheating units, preheating and/or cracking unit and markedly reduces heat transfer efficiency, substantially increases the pressure drop of the hydrocarbon stream and blocks the process flow. This fouling of heat exchangers or other process equipment, such as furnace tubes, is a costly, major, unresolved problem throughout refineries and petrochemical plants since the fouled units must be dismantled, cleaned, and reassembled. Of course, such cleaning operations are not only tedious and costly, but result in a large proportion of "down-time" during which the subject unit is not functioning.
Generally, the carbonaceous deposition can be separated into the lower temperature (&lt;400.degree. C.), long time (minutes to hours) deposits which are hexane insoluble and quinoline soluble and the higher temperature (&gt;750.degree. C.), short time (seconds) coke deposits which are hexane insoluble and quinoline insoluble.
Antifoulant processes to reduce (inhibit) quinoline-soluble carbonaceous deposits include those set forth in: U.S. Pat. No. Re. 26,330 wherein deposit formation in refinery units is inhibited by incorporating in the feed stock a small percentage (usually about 0.0012-0.04 weight percent) of an acylated amine prepared by reacting a hydrocarbon-substituted succinic acid with an alkylene amine; and, U.S. Pat. No. 4,195,976 wherein fouling of process equipment by an oil stream in refinery operations is reduced by incorporating in the feed from 0.001 to 2 wt. % of a bis-oxazoline reaction product of polyisobutenylsuccinic anhydride with a 2,2 disubstituted-2-aminolalkanol, such as tris-hydroxy methylaminomethane.
Approaches to the reduction of coke (carbonaceous coating insoluble in both quinoline and hexane) formation in cracking furnace tubes includes: U.S. Pat. No. 2,621,216 which discloses that coke formation during steam pyrolysis of ethane, propane, or mixtures thereof may be reduced by incorporating from 0.2 to 0.5 volume percent of a sour refinery gas (containing H.sub.2 S) in the pyrolysis feedstock (Col. 7, line 19-75); U.S. Pat. No. 3,437,174 which discloses that incorporation of up to 25% propylene in a naphtha pyrolysis feedstock improves yield selectivity to ethylene without any increase in coking (Col. 2, line 31-48); U.S. Pat. No. 3,536,776 which discloses that thermal cracking of hydrocarbons, may be carried out in a metal-ceramic reaction tube with significantly reduced carbon formation (Col. 2, line 5-13 and line 56-63 and Col. 4, line 27-42); U.S. Pat. No. 3,842,138 which discloses that, in steam cracking, the carbon to hydrogen ratio of the feedstock is important with respect to coking, aromatics can only be tolerated in the feedstock because of their refractory nature, and small amounts of sulfur in feedstock have a favorable effect against coking (Col. 4, line 37 to Col. 5, line 2); and, Green et al in Hydrocarbon Processing, September 1975, pp. 164-168, at page 165 contends that gas oil cracking is disadvantageous compared with naphtha cracking because of lower yields and because higher yields of pyrolysis fuel oil are produced which contain highly aromatic material that is a precursor of tars and coke; whereas, U.S. Pat. No. 4,176,045 discloses that a blending (4 to 20%--see Table 2-5) amounts of low coking liquid hydrocarbon, such as pyrolysis fuel oil with the feedstock prior to introducing the latter into the tubular furnace reduces coke formation.
It is an object of the present invention to inhibit the accumulation of harmful carbonaceous material on the inner surfaces of vessels confining a heated hydrocarbon fluid.
Another object is to disperse the carbonaceous material formed during the preheating of a crude oil and thereby inhibit its accumulation (fouling) on the various parts of the inner wall of the heat exchanger prior to its introduction into a crude distillation unit.
Yet another object is to reduce the amount of downtime, reduce fuel costs and/or increase hydrocarbon throughput in the operation of refinery heat exchangers and cracking units.